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Product Attributes

Introduction

A relay is an electrical control device that opens and closes contacts by controlling coil voltage. The following describes key technical parameters of relays:

• Coil Parameters:
  • Nominal Coil Voltage: The single voltage value (or narrow range) designed to be applied to the coil or input.
  • Pick-up Voltage: The voltage at or below which all contacts must operate (transfer) as the voltage across an unenergized relay is increased.
  • Drop-out Voltage: The voltage at or above which all contacts must return to their unenergized position as the voltage across an energized relay is decreased.
  • Maximum Continuous Voltage: The maximum voltage that can be continuously applied to the coil without causing damage.
  • Nominal Operating Current: The current drawn by the coil at nominal voltage.
  • Nominal Operating Power: The power consumed by the coil at nominal voltage — expressed in watts for DC coils and volt-amperes for AC; calculated as Nominal Power (W or VA) = Nominal Voltage × Nominal Current.
  • Coil Resistance: The DC resistance of the coil for DC-type relays, measured under temperature conditions specified in the catalog.
• Contact Parameters:
  • Contact Form: Indicates the contact mechanism and number of contacts in the contact circuit, including Form A (normally open), Form B (normally closed), and Form C (changeover/transfer).
  • MBB Contact: Abbreviation for Make Before Break — the Form A contact (normally open) closes before the Form B contact (normally closed) opens.
  • Maximum Switching Voltage: The maximum open-circuit voltage that contacts can safely switch; AC and DC maximum values differ in most cases.
  • Maximum Switching Current: The maximum current that contacts can safely switch; AC and DC maximum values may differ.
  • Maximum Switching Power: The upper power limit that contacts can switch.
  • Maximum Carry Current: The maximum current that can safely flow through a closed contact (or before opening) without causing temperatures to exceed the design limits of the relay or other temperature-sensitive components.
  • Minimum Switching Capability: A reference value indicating the lowest level at which low-level loads can be reliably switched; reliability depends on switching frequency, environmental conditions, and the required variation and absolute value of contact resistance.
  • Maximum Switching Capacity: The maximum contact rating listed in the data column for each relay type; represents the interrelationship among maximum switching power, maximum switching voltage, and maximum switching current.
  • Contact Resistance: The combined resistance of the contact interface resistance, terminal resistance, and contact spring resistance when contacts are closed; measured using the voltage drop method.
  • Capacitance: The capacitance between terminals, measured at 1kHz and 20°C (68°F).
• Performance Parameters:
  • Insulation Resistance: The resistance between all mutually isolated conductive parts of the relay — such as between coil and contacts, between open contacts, and between the coil or contacts and any core or frame at ground potential. This value is typically specified as "initial insulation resistance" and may decrease over time.
  • Breakdown Voltage: The maximum voltage a relay can withstand for a specified duration without damage; typically measured at the same points as insulation resistance.
  • Surge Withstand Voltage: The ability of a device to withstand abnormal externally generated power surges, such as those caused by lightning strikes or other phenomena.